The present invention relates to a snap closure for flow medium ducts. Snap closure couplings of that kind are for example used for the coupling of trailers to motor vehicles, wherein one coupling half is arranged firmly on the motor vehicle and the other at the free end of a pressure hose providing the connection to the trailer.
Irrespective of the different constructions of the plug part and sleeve part of a coupling of that kind, both the parts of such a coupling are for simplicity designated as "coupling halves" in the following.
In a flow medium coupling of this kind, which is described in the German Pat. No. 895 396, the closure piece of the one coupling half consists of a valve cone, which is received to be axially movable within a sleevelike housing which is provided with a valve seat surface. Rearwardly this valve cone bears against a closing spring and--in the uncoupled state--is held by this closing spring in closing position with the seat surface; it is also loadable by flow medium pressure when the coupling half is pressure-loaded. The closure piece of the other coupling half is a valve sleeve which is received to be axially movable on a hollow spigot with a seat surface at the front end and likewise--in the uncoupled state--is held by a closing spring in contact against this seat surface as well as being loadable at the rear side, i.e. in closing direction, by flow medium pressure. On coupling of the two halves, the valve sleeve engages with its end face a contact surface enclosing concentrically the valve cone of the other half in the region of the valve seat co-operating with the latter, the head of the hollow spigot receiving the valve sleeve thereagainst onto the valve cone so that the valve cone as well as the valve sleeve are urged into their opening positions during the coupling of both the halves.
The coupling of the halves in the case of the prior known flow medium coupling naturally can succeed only when both coupling halves are relieved of pressure. In many cases of use this prerequisite is, however, not fulfillable or only with difficulty. This is, for example, the case when a trailer equipped with hydraulic brakes is set down with its brakes on and the associated coupling half shall now be coupled with the coupling half which is disposed on the motor vehicle and thus is located on the side of the flow medium pressure source. Concerned in that case is the coupling half equipped with the valve cone, while the coupling half provided with the axially movable coupling sleeve is associated with the sink side. When the sink side stands under pressure loading, a pressure relief must be brought about through awkward manipulations before the two coupling halves can be coupled with each other, which naturally entails flow medium losses, before the valve sleeve is capable of executing the axial displacement which is unavoidable for the performance of the coupling operation.